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RECENT VIDEOS

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11.14.2012
33 mins
ILP Video

Nanomaterials for Hybrid Solar Cells

Silvija Gradecak
Thomas Lord Associate Professor in Materials Science
MIT Department of Materials Science and Engineering
Despite the fact that solar radiation accounts for most of the available renewable energy, only a small portion of it is currently being harnessed, mostly due to the production and installation costs of commercial photovoltaic (PV) devices. Emerging PV devices based on solution-processable conjugated polymers offer opportunities for the production of low-cost solar cells. To obtain high efficiencies of exciton dissociation and high photocurrent, it is desirable to have an interpenetrating network of electron-donor and electron-acceptor components within the device, referred to as a bulk heterojunction (BHJ). However, current limitations of the all-organic PV devices are inefficient hopping charge transport through the discontinuous percolation pathways in the BHJ films, and therefore modest power conversion efficiencies or non-competitive cost in the case of devices based on C60 derivatives.

We have developed a new type of nanowire-based solar cells that are based on organic/inorganic hybrid device structures and demonstrated two distinct hybrid BHJ architectures with enhanced power conversion efficiencies. The first device structure was composed of GaAs nanowires blended with a conjugated polymer poly(3-hexylthiophene) (P3HT) to form a uniform film consisting of dispersed nanowires in a polymer matrix. We observed that above a certain nanowire loading threshold, the nanowires facilitate P3HT molecular ordering, which leads to improved charge transport and yields devices with >2.3% power conversion efficiency. In the second device structure, CdS quantum dots were bound onto crystalline P3HT nanowires through solvent-assisted grafting and ligand exchange, leading to controlled organic-inorganic phase separation and an improved maximum power conversion efficiency of 4.1%.

In both cases, our results clearly demonstrate some of the benefits of organic-inorganic BHJ devices, mostly through enhanced absorption and improved carrier transport in the active region of the device. We have also identified several critical parameters to further boost the device efficiency and enable scalable, cost-efficient production, and these will be discussed.
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11.14.2012
39 mins
ILP Video

Chemo-mechanical Coupling in Electrochemical Energy Conversion and Storage Materials

Harry Tuller
Professor of Ceramics and Electronic Materials
Director, Crystal Physics and Electroceramics Laboratory (CPEL)
MIT Department of Materials Science and Engineering
Many energy related materials rely on transport of ions into and out of electrodes and membranes, for example, Li ions in batteries, O ions in solid oxide fuel cells (SOFCs) and steam electrolyzers, and H ions in hydrogen storage devices. Significant mechanical stresses often accompany these changes in chemical composition, also referred to as chemical expansion. For example, Pr0.1Ce0.9O2-o, a candidate solid oxide fuel cell (SOFC) cathode material, exhibits a >200% increase in its effective thermal expansion coefficient due to oxygen loss upon heating in air. Under the large oxygen partial pressure (pO2) gradient typical of SOFC operation, chemical expansion can result in cracking of electrolyte membranes, and, as a consequence, models have been developed to predict safe operating conditions.

This chemo-mechanical coupling between oxygen stoichiometry and expansion is defined, analogous to thermal expansion, by a chemical coefficient of expansion, which experimentally has been observed to depend on material composition and structure. The atomic origins of the chemical expansion in fluorite and perovskite structured oxides are explored by atomic level computational methods and validated by experimental data including lattice dilation, defect generation and carrier localization. The implications of chemical expansion, including discussion of models developed to predict its impact on SOFCs as well as secondary effects, namely reduction in elastic modulus, as well as a case study of chemical expansion in Pr0.1Ce0.9O2-o, correlating oxygen non-stoichiometry with expansion is presented.
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11.14.2012
29 mins
ILP Video

Advanced Solid State Energy Conversion Devices and Systems

Ivan Celanovic
Principal Research Scientist
MIT Institute for Soldier Nanotechnologies (ISN)
After decades of intense studies focused on cryogenic and room temperature nanophotonics, scientific interest is shifting towards high-temperature nanophotonics focused on (re)inventing the solid-state energy conversion field. These latest advancements are paving the way towards novel high performance energy conversion devices and systems with applications ranging from ultra-portable millimeter scale power sources based on thermophotovoltaics (TPV), new schemes for solar energy conversion, all the way to radioisotope batteries for terrestrial and deep space applications with 30+ year time span without the need for recharging. In this talk we will examine how high-temperature nanophotonics works and illustrate how these material platforms are reshaping many important energy conversion applications.
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11.14.2012
26 mins
ILP Video

Modeling Transport to Discover Advanced Thermoelectric Materials

David J. Singh
Corporate Fellow in the Materials Science and Technology Division
Department of Energy's Oak Ridge National Laboratory
Thermoelectrics are materials that enable low cost solid cooling and power generation systems scaling from very small packages up to large units. A key challenge is to make this technology energy efficient. Thermoelectric performance depends on combinations of properties that do not normally occur in the same material, such as high thermopower in combination with high conductivity and low lattice thermal conductivity in combination with high mobility. While there is no known upper bound on the thermoelectric figure of merit ZT, finding materials with high performance is challenging and requires balancing the properties. Developments in materials modeling, especially for transport properties, allow us to exploit unusual non-text-book electronic and lattice structures to find ways of bypassing these conundrums. Recent examples, including some surprising advances, are described and future directions are discussed.

Work presented here was supported by the Department of Energy, through the S3TEC Energy Frontier Research Center.
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11.14.2012
39 mins
ILP Video

Production in the Innovation Economy (PIE): A New MIT Study on the Current State and Future of U.S. Manufacturing

Olivier de Weck
Associate Professor of Aeronautics and Astronautics and Engineering Systems
Executive Director, MIT Production in the Innovation Economy (PIE) Study
The Production in the Innovation Economy (PIE) project brings together leading MIT faculty from a variety of disciplines to look at the present state and future of U.S. manufacturing. The study's overarching goal is to shed light on how America's great strengths in innovation can be scaled up into new productive capabilities. This talk will present some preliminary findings from PIE and focus on examples of promising manufacturing models based on over 150 company interviews to date.
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